Rotor and compressor

ABSTRACT

A rotor has a main body including a rotation axis, a weight guide recessed in the main body, said weight guide having a weight guide surface and a weight that is accommodated in the weight guide and contacts with and rolls on a weight guiding surface. The weight swings like a pendulum about a second axis. The second axis is parallel to and offset from the rotation axis. The weight guiding surface guides the weight to keep the weight moving within the guiding surface.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a rotor having a weight thatswings like a pendulum and to a compressor that uses the rotor.

[0002] Japanese Laid-Open Patent Publication No. 6-193684 discloses arotor having a flywheel, in which a weight guide (weight receptacle) isdefined. A weight (damper mass) is accommodated in the weight guide(weight receptacle). The weight rolls in the weight receptacle. Aprojection having a rectangular cross-section is formed in one of theweight guide and the weight. A groove having a rectangular cross sectionis formed in the other one of the guide and the weight. The projectionand the groove extend along the rolling direction of the weight andengage with each other. The engagement of the projection and the grooveprevents the weight from moving in the axial direction of the rotor.Thus, the weight does not collide with the walls of the weight guide,which suppresses the noise due to collision.

[0003] However, a clearance must be created between the projection andthe groove to allow the weight to swing like a pendulum. The clearancepermits the weight to move in the axial direction. The weight thereforechatters and produces noise.

SUMMARY OF THE INVENTION

[0004] Accordingly, it is a major objective of the present invention toprovide a rotor that suppresses resonance by pendulum-like motion of aweight accommodated in a weight guide and reduces noise produced bycollision of the weight against the walls of the receptacle.

[0005] It is a further objective of the present invention to provide acompressor that uses the rotor.

[0006] To achieve the foregoing and other objectives and in accordancewith the purpose of the present invention, a rotor has a main bodyincluding a rotation axis, a weight guide recessed in the main body,said weight guide having a weight guide surface and a weight that isaccommodated in the weight guide and contacts with and rolls on a weightguiding surface. The weight swings like a pendulum about a second axis.The second axis is parallel to and offset from the rotation axis. Theweight guiding surface guides the weight to keep the weight movingwithin the guiding surface.

[0007] Other aspects and advantages of the invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention, together with objects and advantages thereof, maybest be understood by reference to the following description of thepresently preferred embodiments together with the accompanying drawingsin which:

[0009]FIG. 1 is a cross-sectional view illustrating a compressor havinga pulley according to one embodiment of the present invention;

[0010]FIG. 2(a) is a front view illustrating the pulley of FIG. 1;

[0011]FIG. 2(b) is a cross-sectional view taken along line b-b of FIG.2(a);

[0012]FIG. 3(a) is an enlarged partial cross-sectional view illustratinga groove and a roller (weight) according to another embodiment;

[0013]FIG. 3(b) is an enlarged partial cross-sectional view illustratinga groove and a roller (weight) according to another embodiment;

[0014]FIG. 3(c) is an enlarged partial cross-sectional view illustratinga groove and a roller (weight) according to another embodiment; and

[0015]FIG. 3(d) is an enlarged partial cross-sectional view illustratinga groove and a roller (weight) according to another embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A compressor C according to one embodiment of the presentinvention will now be described with reference to FIGS. 1 to 2(b). Theleft end of the compressor C in FIG. 1 is defined as the front of thecompressor, and the right end is defined as the rear of the compressorC.

[0017] As shown in FIG. 1, the compressor C includes a cylinder block11, a front housing member 12, a valve plate assembly 13, and a rearhousing member 14. The front housing member 12 is secured to the frontend of the cylinder block 11. The rear housing member 14 is secured tothe rear end of the cylinder block 11 with the valve plate assembly 13in between. The cylinder block 11, the front housing 12, the valve plateassembly 13, and the rear housing member 14 form the housing of thecompressor C.

[0018] The cylinder block 11 and the front housing member 12 define acrank chamber 15 in between.

[0019] A rotary shaft, which is a drive shaft 16 in this embodiment, ishoused in the compressor housing and extends through the crank chamber15.

[0020] A cylindrical support 40 is formed at the front end of the fronthousing member 12. The front end portion of the drive shaft 16 extendsthrough the front wall of the front housing member 12 and is located inthe cylindrical support 40. The front end portion of the drive shaft 16is coupled to an external drive source, which is a vehicular engine E inthis embodiment, by a rotor, which is a pulley 17 in this embodiment,and a belt 18 wound around the pulley 17.

[0021] A lug plate 19 is coupled to the drive shaft 16 and is located inthe crank chamber 15. The lug plate 19 rotates integrally with the driveshaft 16. A cam plate, which is a swash plate 20 in this embodiment, ishoused in the crank chamber 15. The swash plate 20 slides along andinclines with respect to the drive shaft 16. The swash plate 20 iscoupled to the lug plate 19 by the hinge mechanism 21. The lug plate 19permits the swash plate 20 to rotate integrally with the drive shaft 16and to incline with respect to the drive shaft 16 while sliding alongthe rotation axis of the drive shaft 16.

[0022] A snap ring 22 is fitted about the drive shaft 16. A spring 23extends between the snap ring 22 and the swash plate 20. The snap ring22 and the spring 23 limit the minimum inclination angle of the swashplate 20. At the minimum inclination angle of the swash plate 20, theangle defined by the swash plate 20 and the axis of the drive shaft 16is closest to ninety degrees.

[0023] Cylinder bores 24 (only one is shown in FIG. 1) are formed in thecylinder block 11. The cylinder bores 24 are located about the rotationaxis of the drive shaft 16. A single-headed piston 25 is reciprocallyhoused in each cylinder bore 24. The front and rear openings of eachcylinder bore 24 are closed by the associated piston 25 and the valveplate assembly 13. A compression chamber is defined in each cylinderbore 24. The volume of the compression chamber changes according to thereciprocation of the corresponding piston 24. Each piston 25 is coupledto the peripheral portion of the swash plate 20 by a pair of shoes 26.When the swash plate 20 is rotated by rotation of the drive shaft 16,the shoes 26 converts the rotation into reciprocation of each piston 25.

[0024] The drive shaft 16, the lug plate 19, the swash plate 20, thehinge mechanism 21, the pistons 25, and the shoes 26 form a piston typecompression mechanism.

[0025] Sets of suction ports 29 and suction valve flaps 30 and sets ofdischarge ports 31 and discharge valve flaps 32 are formed in the valveplate assembly 13. Each set of the suction port 29 and the correspondingsuction valve flap 30 and each set of the discharge port 31 and thecorresponding discharge valve flap 30 correspond to one of the cylinderbores 24 (compression chambers).

[0026] A suction chamber 27 and a discharge chamber 28 are defined inthe rear housing member 14. The front ends of the suction chamber 27 andthe discharge chamber 28 are closed by the valve plate assembly 13. Aseach piston 25 moves from the top dead center position to the bottomdead center position, refrigerant gas is drawn into the correspondingcylinder bore 24 (compression chamber) through the corresponding suctionport 29 while flexing the suction valve flap 30 to an open position. Lowpressure refrigerant gas that is drawn into the cylinder bore 24 iscompressed to a predetermined pressure as the piston 25 is moved fromthe bottom dead center position to the top dead center position. Then,the gas is discharged to the discharge chamber 28 through thecorresponding discharge port 31 while flexing the discharge valve flap32 to an open position.

[0027] The suction chamber 27 is connected to the discharge chamber 28by an external refrigerant circuit (not shown). Refrigerant that isdischarged from the discharge chamber 28 flows into the externalrefrigerant circuit. The external refrigerant circuit performs heatexchange using the refrigerant. When discharged from the externalrefrigerant circuit, the refrigerant is drawn into the suction chamber27. Then, the refrigerant is drawn into each cylinder bore 24 to becompressed again.

[0028] A bleed passage 33 is formed in the housing to connect the crankchamber 15 with the suction chamber 27. A supply passage 34 is formed inthe housing to connect the discharge chamber 28 with the crank chamber15. A control valve 35 is located in the supply passage 34 to regulatethe opening degree of the supply passage 34. The opening of the controlvalve 35 is adjusted to control the flow rate of highly pressurized gassupplied to the crank chamber 15 through the supply passage 34.

[0029] The pressure in the crank chamber 15 (crank chamber pressure Pc)is determined by the ratio of the gas supplied to the crank chamber 15through the supply passage 34 and the flow rate of refrigerant gasconducted out from the crank chamber 15 through the bleed passage 33. Asthe crank chamber pressure Pc varies, the difference between the crankchamber pressure Pc and the pressure in the compression chambers varies,which changes the inclination angle of the swash plate 20. Accordingly,the stroke of each piston 25, or the compressor displacement, is varied.

[0030] As shown in FIGS. 1 and 2(b), the pulley 17 is located about androtatably supported by the support cylinder 40 with a bearing 41. Thepulley 17 is also fixed to the drive shaft 16 to rotate integrally withthe drive shaft 16.

[0031] As shown in FIGS. 1 and 2, the pulley 17 includes a main body 42(rotor main body). The pulley main body 42 has a boss 43, which isfitted about the outer ring of the bearing 41, and a belt receivingportion 44, which is wound around the belt 18. Two weight receptacles 45are formed between the boss 43 and the belt receiving portion 44. Theweight receptacles 45 are symmetrically arranged with respect to therotation axis of the main body 42.

[0032] A weight guiding surface 46 is formed in each weight receptacle45. A cross section of the weight guiding surface 46 along a planeperpendicular to the rotation axis of the pulley main body 42 isarcuate. The center of curvature of the weight guiding surface 46coincides with a line that extends parallel to and is spaced from therotation axis of the pulley main body 42 by a predetermined distance R₁.Each weight guiding surface 46 is formed at a side of the correspondingweight receptacle 45 that is close to the periphery of the pulley mainbody 42.

[0033] A weight guiding path, which is a groove 46A in this embodiment,extends along the circumferential direction of each weight guidingsurface 46, or in the direction along which a weight ball 48 rolls. Thecross section of the groove 46A along a plane containing the center ofcurvature of the weight guiding surface 46 (cross section shown in FIGS.1 and 2(b)) is arcuate. The radius of curvature of each groove 46Arepresented by r₁. Arcuate inner surfaces 46B are formed at the frontand rear sides of the groove 46A in each weight guiding surface 46. Thearcuate inner surfaces 46B form parts of the inner surface of a commonimaginary cylinder.

[0034] An auxiliary guiding surface 47 is formed in each weightreceptacle 45. The auxiliary guiding surface 47 is separated from thearcuate inner surfaces 46B toward the axis of the pulley main body 42 bya predetermined distance. As viewed from the front side of thecompressor C, each weight receptacle 45 appears as an arc having aconstant width with its middle portion located closer to the peripheryof the pulley main body 42 than its ends. As viewed from the front sideof the compressor C, each weight receptacle 45 is symmetrical withrespect to an imaginary line that contains the rotation axis of thepulley main body 42 and the center of the corresponding imaginarycylinder.

[0035] Each of the grooves 46A has a substantially U-shape in crosssection. In other words, the edge of the groove 46A extending to formthe U-shape is inclined with respect to the axis of the pendulum motion.

[0036] A weight, which is a rigid weight ball 48 in this embodiment, isaccommodated in each weight receptacle 45. The mass of each weight ball48 is referred to as m₁. The diameter d₁ of each weight ball 48 isslightly less than the distance between the arcuate inner surfaces 46Band the auxiliary guiding surface 47. The diameter d₁ is equal to thedoubled radius r₁ of curvature of the groove 46A. The axial size of eachgroove 46A is slightly less than the diameter d₁ of the weight ball 48so that substantially a half of the weight ball 48 is fitted in thegroove 46A. Each weight ball 48 linearly contacts the correspondinggroove 46A with a part (substantially a half) fitted in the groove 46A.In this state, the weight ball 48 moves along the groove 46A.

[0037] An annular cover 49 is fixed to the pulley 17 by screws (notshown) to cover the receptacles 45. Even if the weight balls 48 aredislocated from the grooves 46A, the cover 49 prevents the weight balls48 from falling off the receptacles 45. The receptacles 45 and the cover49 form weight guides.

[0038] When the compressor C is being driven by the engine E, or whenthe drive shaft 16 is rotating, the weight balls 48 linearly contact thegrooves 46A due to the centrifugal force (see FIGS. 1 to 2(b)). If atorque is generated by rotational fluctuation of the drive shaft 16,each weight ball 48 reciprocates along the groove 46A in thecorresponding weight receptacle 45. In other words, the weight ball 48,or its center of gravity, swings like a pendulum about the center ofcurvature of the corresponding weight guiding surface 46. That is, eachweight ball 48 acts as a centrifugal pendulum when the compressor C isbeing driven by the engine E.

[0039] The size and weight of the weight balls 48 and the locations ofthe weight balls 48 in the pulley main body 42 are determined such thatthe torque fluctuation is suppressed by pendulum motion of the weightballs 48.

[0040] The settings of the weight balls 48, which function ascentrifugal pendulums, will now be described.

[0041] The weight balls 48 suppress torque fluctuation. Specifically,each weight ball 48 suppresses a fluctuation band at a frequency that isequal to the characteristic frequency of the weight ball 48 (centrifugalpendulum). Therefore, the location, the size, and the weight of eachweight ball 48 are determined such that the characteristic frequency ofthe weight ball 48 is set equal to the frequency of a peak component ofthe torque fluctuation. Accordingly, the amplitude of the peak componentis suppressed, and the influence of the torque fluctuation iseffectively reduced. Peak components of the torque fluctuation representthe peaks of the fluctuation band, or the components of rotation order.

[0042] The frequency of the torque fluctuation and the characteristicfrequency of the weight balls 48 are proportional to the angularvelocity ω₁ of the drive shaft 16, which corresponds to the speed of thedrive shaft 16. The frequency of the torque fluctuation when its band isgreatest is represented by the product of the rotation speed of thedrive shaft 16 per unit time (ω₁/2) and the number N of the cylinderbore 24. That is, the frequency is represented by the formula (ω₁/2π) N.

[0043] Through experiments, it was confirmed that an nth greatest peak(n is a natural number) of the torque fluctuation has a value equal to aproduct n·(ω₁/2π)·N.

[0044] The characteristic frequency of the weight balls 48 is obtainedby multiplying the rotation speed of the drive shaft 16 per unit time(ω₁/2π) with the square root of the ratio R/r. The sign R represents thedistance between the rotation axis of the pulley main body 42 and theaxis of the pendulum motion of each weight ball 48. The sign rrepresents the distance between the axis of the pendulum motion of eachweight ball 48 and the center of gravity of the weight ball 48.

[0045] Therefore, by equalizing the square root of the ratio R/r withthe product n·N, the characteristic frequency of the weight balls 48 areequal to the frequency of the nth greatest peak of the torquefluctuation. Accordingly, the torque fluctuation at the nth greatestpeak is suppressed.

[0046] To suppress the greatest peak of the torque fluctuation, thevalues of the distances R and r are determined such that the square rootof the ratio R/r is equal to N, or the value of the product n·N when nis one.

[0047] The torque produced about the rotation axis of the pulley mainbody 42 by the weight balls 48 is represented by a sign T. Toeffectively reduce the torque fluctuation by the pendulum motion of theweight balls 48, the torque T needs to counter the torque fluctuationand the range of the torque T needs to be equal to the range of thefluctuation. When the frequency of a peak of the torque fluctuation isequal to the characteristic frequency of the weight balls 48, the torqueT is represented by the following equation.

T=m·(ω_(a))²·(R+r)·R·φ  (Equation 1)

[0048] In the equation 1, the sign m represents the total mass of theweight balls 48 (m=2m₁), and ω_(a) represents the average angularvelocity of the swing balls when the balls swing in a minute angle φ.

[0049] In this embodiment, the mass m is maximized to minimize thevalues R, r, and φ, so that the size of the pulley main body 42 isminimized, and the torque T is maximized.

[0050] The center of curvature of each weight guiding surface 46coincides with the axis of the pendulum motion of the corresponding ball48. That is, the distance R₁ between the rotation axis of the pulleymain body 42 and the center of curvature of each weight guiding surface46 corresponds to the distance R.

[0051] The settings are determined by regarding the weight ball 48 as aparticle at the center of gravity.

[0052] The operation of the compressor C will now be described.

[0053] When the power of the engine E is supplied to the drive shaft 16through the pulley 17, the swash plate 20 rotates integrally with thedrive shaft 16. As the swash plate 20 rotates, each piston 25reciprocates in the associated cylinder bore 24 by a strokecorresponding to the inclination angle of the swash plate 20. As aresult, suction, compression and discharge of refrigerant gas arerepeated in the cylinder bores 24.

[0054] If the opening degree of the control valve 35 is decreased, theflow rate of highly pressurized gas supplied to the crank chamber 15from the discharge chamber 28 through the supply passage 34 isdecreased. Accordingly, the crank chamber pressure Pc is lowered and theinclination angle of the swash plate 20 is increased. As a result, thedisplacement of the compressor C is increased. If the opening degree ofthe control valve 35 is increased, the flow rate of highly pressurizedgas supplied to the crank chamber 15 from the discharge chamber 28through the supply passage 34 is increased. Accordingly, the crankchamber pressure Pc is raised and the inclination angle of the swashplate 20 is decreased. As a result, the displacement of the compressor Cis decreased.

[0055] During rotation of the drive shaft 16, the compression reactionforce of refrigerant and reaction force of reciprocation of the pistons25 are transmitted to the drive shaft 16 through the swash plate 20 andthe hinge mechanism 21, which torsionally (rotationally) vibrates thedrive shaft 16. The torsional vibrations generate torque fluctuation.The torque fluctuation causes the compressor C to resonate. The torquefluctuation also produces resonance between the compressor C and rotarymachines (the engine E and auxiliary devices), which are connected tothe pulley 17 by the belt 18.

[0056] When the torque fluctuation is produced, the weight balls 48start swinging like pendulums. The pendulum motion of the weight balls48 produces torque about the rotation axis of the pulley main body 42.The produced torque suppresses the torque fluctuation. Thecharacteristic frequency of each weight ball 48 is equal to thefrequency of the greatest peak of the torque fluctuation. Therefore, thepeak of the torque fluctuation is suppressed, which effectively reducesthe torque fluctuation of the pulley 17. As a result, the resonanceproduced by the torque fluctuation is effectively suppressed.

[0057] The present embodiment has the following advantages.

[0058] (1) The weight balls 48 are provided in the pulley main body 42.The axis of each weight ball 48 is spaced from the rotation axis of thepulley main body 42 by the predetermined distance R₁ and is parallel tothe rotation axis of the pulley main body 42. Each weight ball 48 swingslike a pendulum about its axis. The pendulum motion of the weight balls48 suppresses the torsional vibration of the pulley 17, which suppressesresonance produced in the compressor C. Further, the pendulum motionsuppresses resonance produced between the compressor C and the rotarymachines that are coupled to the pulley 17 by the belt 18.

[0059] (2) The groove 46A is formed in each weight guiding surface 46. Across section of each groove 46A along a plane containing the axis ofpendulum motion of the corresponding weight ball 48 is substantiallyU-shaped. In the other words, the cross section of the groove 46A is notparallel, or inclined to the axis of the pendulum motion. The weightball 48 is pressed against the groove 46A by centrifugal force, whichprevents the weight ball 48 from moving in the axial direction.Therefore, the weight ball 48 is prevented from colliding with the innerwalls of the weight guide, which reduces the noise.

[0060] (3) Each groove 46A, which contacts one of the weight balls 48,has an arcuate cross section along a plane containing the axis of thependulum motion. The radius r₁ of curvature of the groove 46A is equalto a half of the diameter d₁ of the weight ball 48, or the radius of theweight ball 48. Therefore, when the weight ball 48 swings along thegroove 46A, there is no clearance between the weight ball 48 and thegroove 46A that permits the weight ball 48 to move axially.

[0061] (4) The axial size of each groove 46A is slightly less than thediameter d₁ of the weight ball 48 so that substantially a half of theweight ball 48 is fitted in the groove 46A. Compared to a case in whichthe axial size of the groove 46A is narrower, a greater part of theweight ball 48 is located in the groove 46A when the weight ball 48swings along the groove 46A. Therefore, the weight ball 48 is lesslikely to be dislocated.

[0062] It should be apparent to those skilled in the art that thepresent invention may be embodied in many other specific forms withoutdeparting from the spirit or scope of the invention. Particularly, itshould be understood that the invention may be embodied in the followingforms.

[0063] In the embodiment of FIGS. 1 to 2(b), the cross section of eachgroove 46A along the plane containing the axis of the pendulum motion isarcuate. The axial size of each groove 46A is determined such that ahalf of the corresponding weight ball 48 is received by the groove 46A.However, the axial size of each groove 46A may be changed. For example,the axial size of each groove 46A may be determined such that a smallerportion of the weight ball 48 is received by the groove 46A.

[0064] In the embodiment of FIGS. 1 to 2(b), the weight guides (theweight receptacles 45) are arcuate and have a constant width when viewedfrom the front side of the compressor C. However, the shape of eachweight receptacle 45 may be changed. As long as each weight receptacle45 has a weight guiding surface, the shape of the weight receptacle 45may be changed, for example, to a circular shape.

[0065] In the embodiment of FIGS. 1 to 2(b), the diameter d₁ of eachweight ball 48 is equal to the doubled radius r₁ of curvature of thegroove 46A. However, the diameter d₁ may be changed. For example, thediameter d₁ may be less than the doubled radius r₁. In this case, evenif an external force in the axial direction of the pendulum motion isapplied to the weight ball 48, the weight ball 48 remains contacting thesurface of the groove 46A and reciprocates along the width of the groove46A. That is, noise due to collision between the weight ball 48 and thegroove 46A is prevented. If the diameter d₁ is greater than the doubledradius r₁, the weight ball 48 is prevented from moving in the axialdirection by the edges of the groove 46A.

[0066] In the embodiment of FIGS. 1 to 2(b), each groove 46A, whichcontacts the weight ball 48, has an arcuate cross section along a planecontaining the axis of the pendulum motion. However, the cross sectionof the groove 46A may be U-shaped. In other words, the cross section ofthe groove 46A may be changed as long as there is no clearance betweenthe weight ball 48 and the groove 46A that permits the weight ball 48 tomove axially when the weight ball 48 swings along the groove 46A.

[0067] In the embodiment of FIGS. 1 to 2(b), the cross section of partof each weight guiding surface 46 along the plane containing the axis ofthe pendulum motion is arcuate. However, at least part of each weightguiding surface may include an inclined surface and formed as aprojection or a groove that extends along the reciprocation direction ofthe weight. In this case, the outer shape of the weight is preferablyshaped to fit the projection or the groove formed in the weightreceptacle. FIGS. 3(a) to 3(c) describe weight receptacles of suchembodiments. FIGS. 3(a) to 3(c) are cross-sectional views of the cover49, weight receptacles 51, 53, 55 forming weight guides, and weights,which are rollers (52, 54, 56) located in the weight receptacles (51,53, 55) taken along a plane containing the axis of the pendulum motionof the rollers (52, 54, 56).

[0068] The weight receptacle 51 shown in FIG. 3(a) has a weight guidingsurface 51A. Inclined sections 51B, 51C are formed in the axial ends ofthe weight guiding surface 51A. Therefore, the weight guiding surface51A is formed as a groove extending along the reciprocation direction ofthe substantially cylindrical roller 52. An arcuate surface 51D isformed between the inclined section 51B, 51C. The arcuate surface 51D isa part of an imaginary cylinder the center of which coincides with theaxis of the pendulum motion. The roller 52 has an annular projection52A. The projection 52A fits in the groove defined by the inclinedsections 51B, 51C.

[0069] The weight receptacle 53 shown in FIG. 3(b) has a weight guidingsurface 53A. Inclined sections 53B, 53C are formed in the guidingsurface 53A. Therefore, the weight guiding surface 53A is formed as agroove extending along the reciprocation direction of the roller 54. Theinclined sections 53B, 53C are adjacent to each other. The roller 54 hasan annular projection 54A. The projection 54A fits in the groove definedby the inclined sections 53B, 53C.

[0070] The weight receptacle 55 shown in FIG. 3(c) has a weight guidingsurface 55A. Inclined sections 55B, 55C are formed in the guidingsurface 55A. Therefore, the guiding surface 55A is formed as aprojection extending along the reciprocation direction of the roller 56.The inclined sections 55B, 55C are adjacent to each other. The roller 56has an annular groove 56A. The groove 56A fits on the projection definedby the inclined sections 55B, 55C. In the embodiments of FIGS. 3(a) to3(c), the engagement between the weight and the groove or the projectionprevents the weight from being displaced in the axial direction.Therefore, the weight is prevented from colliding with the inner wallsof the weight guide.

[0071] In the embodiment of FIG. 3(c), the pulley main body 42 is formedby coupling two pieces the boundary of which is shown by broken lines.The pulley pieces are molded by dies that move along the axial directionof the pulley main body 42 and then coupled to each other. Therefore,undercuts are not formed. This facilitates the forming of the pulleymain body 42 and reduces the cost.

[0072] The cross section of the weight guiding surface along the planecontaining the axis of the pendulum motion may form a line that isinclined relative to the axis of the pendulum motion. FIGS. 3(d)describes such an embodiment.

[0073] FIGS. 3(d) is cross-sectional view of the cover 49, a weightreceptacle 57 forming a weight guide, and a weight, which is a roller58, located in the weight receptacles 57 taken along the planecontaining the axis of the pendulum motion of the roller 58. The weightreceptacle 57 includes a roller guiding surface 57A. The roller guidingsurface 57A is inclined that the weight receptacle 57 is radiallywidened toward the open end (the left end as viewed in FIG. 3(d)). Theroller 58 swings along the guide 57A like a pendulum. The roller 58 isformed as a frustum. The circumference of the roller 58 is inclined suchthat the roller 58 linearly contacts the guide 57A.

[0074] When the roller 58 is swinging along the guiding surface 57A, thefront end (the left end as viewed in FIG. 3(d)) of the roller 58contacts the cover 49, which is located at the open end of the weightreceptacle 57. The contact between the guiding surface 57A and thecircumference of the roller 58 prevents the roller 58 from movingrearward (rightward as viewed in FIG. 3(d)). Also, the contact betweenthe cover 49 and the front surface of the roller 58 prevents the roller58 from moving forward. Therefore, the weight is prevented fromcolliding with the inner walls of the weight guide.

[0075] In the embodiment of FIGS. 3(d), the pulley main body 42 ismolded by dies that move along the axial direction of the pulley mainbody 42. The guide 57A is formed when the pulley main body 42 is molded.Therefore, undercuts are not formed. This facilitates the forming of thepulley main body 42 and reduces the cost.

[0076] In the embodiment of FIG. 3(d), the weight receptacle 57 isradially widened toward the open end. However, the weight receptacle 57may be narrowed toward the open end. In this case, the weight (roller)is prevented from moving in the axial direction by the guiding surfaceand the wall that faces the cover 49.

[0077] In the embodiment of FIG. 3(d), the weight is formed like afulcrum linearly contacts the guiding surface. However, the weight maybe spherical and in point contact with the guiding surface.

[0078] For example, an axial projection 61 may be formed on either sideof the weight (52) as illustrated by broken lines in FIG. 3(a). In thiscase, when the weight moves in the axial direction, the projections 61contact the inner walls of the weight guide. Therefore, compared to acase where there is no axial projections like projections 61 and theentire axial surfaces contact the inner walls when the weight movesaxially, the weight having the projections 61 contacts the inner wallsat smaller areas and produces less noise. In other words, the noise isreduced.

[0079] In the embodiment of FIGS. 1 to 2(b), the square root of theratio R/r is equal to N, which is the value of n·N when the n is one.However, the square root of the ratio R/r may be the value of n·N when nis a natural number that is greater than one.

[0080] In the embodiment of FIGS. 1 to 2(b), the pulley main body 42 hastwo weight guides each accommodating a weight. However, the number ofthe weight guides may be changed. The number of the weight guides neednot correspond to the number of the cylinder bores of the compressor C.If the pulley main body 42 has only one mass, the pulley main body 42may have a balancer such as a weight or a thinned portion to prevent thecenter of gravity of the pulley main body 42 from being displaced.

[0081] If the pulley main body 42 has two or more weights, the ratio R/rof the weights may be different. Since there is two or more values ofthe ratios R/r of the weights, the bands of two or more peaks (rotationorder) of the torque fluctuation are suppressed. In this case, thevalues n are preferably selected from numbers in order from one. Forexample, when three numbers are selected, one, two and three arepreferably used. Accordingly, the square roots of the ratios R/rcorrespond to the numbers represented by the products n·N, in which thevalue n is one, two and three. Therefore, the three greatest peaks ofthe torque fluctuation are suppressed. That is, the resonance iseffectively suppressed.

[0082] In the illustrated embodiments, the settings are determined byregarding each weight as a particle at the center of gravity. However,the settings are preferably determined by taking the inertial mass ofeach weight into consideration. For example, in the case of the weightballs 48, the settings are preferably made based on the ratio 5R/7rinstead on the ratio R/r so that the inertial mass of the weight balls48 are taken into consideration. When the frequency of a peak of thetorque fluctuation is equal to the characteristic frequency of theweight balls 48, the torque T is represented by the following equation.

T=(7/5)·m·(ω_(a))²·(R+r)·R·φ  (Equation 2)

[0083] If the weights are formed in a shape other than spherical shapes,the settings are preferably made by taking the inertial mass of theweight into consideration so that the resonance is effectivelysuppressed.

[0084] In the illustrated embodiments, the pulley 17 is used for thecompressor C, which has the single headed pistons 25. However, thepulley 17 may be used for a compressor that has double-headed pistons.In this type of compressor, cylinder bores are formed on either side ofa crank chamber and each piston compresses gas in the corresponding pairof the cylinder bores.

[0085] In the illustrated embodiment, the cam plate (the swash plate 20)rotates integrally with the drive shaft 16. However, the presentinvention may be applied to a compressor in which a cam plate rotatesrelative to a drive shaft. For example, the present invention may beapplied to a wobble type compressor.

[0086] The present invention may be applied to a fixed displacement typecompressor, in which the stroke of the pistons are not variable.

[0087] In the illustrated embodiments, the present invention is appliedto a reciprocal piston type compressor. However, the present inventionmay be applied to rotary compressors such as a scroll type compressor

[0088] The present invention may be applied to any type or rotor otherthan pulley. For example, the present invention may be applied to asprocket or a gear.

[0089] The present invention may be applied to a rotating member locatedin the housing of the compressor C. For example, the lug plate 19, whichis located in the housing and coupled to the drive shaft 16, may havethe weights to suppress the rotational vibrations produced in the driveshaft 16. In this case, resonance in the compressor C is suppressed andnoise produced by collision between the weights and the weight guides isreduced. Moreover, since the weights are located in the compressor C,little noise escapes the compressor C.

[0090] In the illustrated embodiments, the present invention is appliedto the compressor C. However, the present invention may be applied toother apparatuses. Specifically, the present invention may be applied toany apparatus in which rotational vibration is produced.

[0091] The axis of the pendulum motion of each weight need not beparallel to the rotation axis of the rotor. Specifically, the axis ofthe pendulum motion may be inclined relative to the rotation axis of therotor in a range in which the maximum torque fluctuation is suppressedby a desirable degree.

[0092] Therefore, the present examples and embodiments are to beconsidered as illustrative and not restrictive and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalence of the appended claims.

1. A rotor comprising: a main body having a rotation axis; a weightguide recessed in the main body, said weight guide having a weight guidesurface; and a weight that is accommodated in the weight guide andcontacts with and rolls on a weight guiding surface, wherein the weightswings like a pendulum about a second axis, and wherein the second axisis parallel to and offset from the rotation axis; wherein the weightguiding surface guides the weight to keep the weight moving within theguiding surface.
 2. The rotor according to claim 1, wherein the weightguide surface has a U-shaped cross-sectional surface along a plane thatcontains the second axis.
 3. The rotor according to claim 1, wherein theweight guide surface has an inclined cross-sectional surface along aplane that contains the second axis.
 4. The rotor according to claim 1,wherein an annular groove or an annular projection is formed in thecircumferential portion of the weight, and wherein a weight guiding pathengaging with the circumferential portion of the weight is formed in theweight guiding surface, the weight guiding path being a projection or agroove.
 5. The rotor according to claim 4, wherein an inclined sectionis formed in at least part of the weight guiding surface, and whereinthe weight guiding surface includes an inclined section.
 6. The rotoraccording to claim 4, wherein the weight guiding path on the weightguiding surface is a projection, and wherein the circumferential portionof the weight has an annular groove.
 7. A rotor comprising: a main bodyhaving a rotation axis; a weight guide formed in the main body, saidweight guide having an arcuate shape in a cross-section along a planeperpendicular to the rotation axis; and a weight accommodated in theweight guide, the weight having a circular cross-section, wherein theweight rolls along a weight guiding surface and swings like a pendulumabout a second axis, and wherein the second axis is separated from therotation axis by a predetermined distance and is parallel to therotation axis; wherein the weight guiding surface has a portion thatcontacts the weight, wherein said contacting portion has across-sectional surface along a plane containing the second axis, saidcross-section surface being substantially U-shaped such that the weightis prevented from moving toward the second axis.
 8. The rotor accordingto claim 7, wherein an annular groove or an annular projection is formedin the circumferential portion of the weight, and wherein a weightguiding path engaging with the circumferential portion of the weight isformed in the weight guiding surface, the weight guiding path being aprojection or a groove.
 9. The rotor according to claim 8, wherein aninclined section is formed in at least part of the weight guidingsurface, and wherein weight guiding surface includes an inclinedsection.
 10. The rotor according to claim 8, wherein the weight guidingpath on the weight guiding surface is a projection, and wherein thecircumferential portion of the weight has an annular groove.
 11. A rotorcomprising: a main body haning a rotation axis; a weight guide formed inthe main body, said weight guide having an arcuate shape in across-section along a plane perpendicular to the rotation axis; a weightaccommodated in the weight guide, the weight having a circularcross-section, wherein the weight rolls along a weight guiding surfaceand swings like a pendulum about a second axis, and wherein the secondaxis is separated from the rotation axis by a predetermined distance andis parallel to the rotation axis; wherein the weight guiding surface hasa portion that contacts the weight, wherein the contacting portion has across-sectional surface along a plane containing the second axis, saidcross-section surface being substantially U-shaped such that the weightis prevented from moving toward the second axis; an annular groove or anannular projection formed in the circumferential portion of the weight;and a weight guiding path formed in the weight guiding surface, theweight guiding path engaging with the circumferential portion of theweight, wherein the weight guiding path being a projection or a groove.12. The rotor according to claim 11, wherein an inclined section isformed in at least part of the weight guiding surface, and wherein theweight guiding surface includes an inclined section.
 13. The rotoraccording to claim 12, wherein the weight guiding path on the weightguiding surface is a projection, and wherein the circumferential portionof the weight has an annular groove.
 14. A compressor driven by power ofa vehicle engine, comprising: a pulley receiving power from the engine;a weight guide formed in the pulley, wherein the weight guide has anarcuate shape in a cross-section along a plane perpendicular to therotation axis; and a weight accommodated in the weight guide, the weighthaving a circular cross-section, wherein the weight rolls along a weightguiding surface and swings like a pendulum about a second axis, andwherein the second axis is separated from the rotation axis by apredetermined distance and is parallel to the rotation axis; wherein theweight guiding surface has a portion that contacts the weight, whereinthe contacting portion has a cross-sectional surface along a plane thatcontains the second axis, the cross-section surface being inclinedrelative to the second axis such that the weight is prevented frommoving toward the second axis.
 15. The compressor according to claim 14,wherein the cross-section surface of the contacting portion issubstantially U-shaped.
 16. The compressor according to claim 14,wherein an annular groove or an annular projection is formed in thecircumferential portion of the weight, and wherein a weight guiding pathengaging with the circumferential portion of the weight is formed in theweight guiding surface, the weight guiding path being a projection or agroove.
 17. The compressor according to claim 16, wherein an inclinedsection is formed in at least part of the weight guiding surface, andwherein the weight guiding surface includes an inclined section.
 18. Arotor comprising: a main body having a rotation axis; a weight guideformed in the main body, said weight guide having an arcuate shape in across-section along a plane perpendicular to the rotation axis, saidweight guide having a weight guide surface; and a weight accommodated inthe weight guide, the weight having a circular cross-section, whereinthe weight rolls along a weight guiding surface and swings like apendulum about a second axis, and wherein the second axis is separatedfrom the rotation axis by a predetermined distance and is parallel tothe rotation axis; wherein the weight guiding surface has a portion thatcontacts the weight, wherein said contacting portion has across-sectional surface along a plane that contains the second axis,said cross-sectional surface is inclined relative to the second axissuch that the weight is prevented from moving in the direction of thesecond axis.